Conventional semiconductor manufacturing facilities handle 300 mm wafers transport containers that typically store twenty-five wafers per container. These containers are commonly referred to as Standard Mechanical Interface (SMIF) pods or Front Opening Universal Pods (FOUPs). The various processing tools, stockers and material handling systems within the fabrication facility are designed to operate with these 300 mm SMIF pods and FOUPs.
After a load port opens the FOUP and makes the wafers within the FOUP accessible, the processing tool processes all the wafers stored in the FOUP. The FOUP will not be removed from the load port until all the wafers are processed and the FOUP door is replaced. Thus, the cycle time for each FOUP is dependent on the number of wafers stored in the FOUP. Improvements in factory cycle time can be gained by reducing lot size of each FOUP from twenty-five wafers per FOUP to, for example, six wafers per FOUP.
However, tool starvation becomes a bigger problem when utilizing smaller lot FOUPs. The time for the material transport system to remove a completed pod and replace it with a new one must be much faster, or else the tool will sometimes have to wait to receive material to processes. One solution to help minimize the time a processing tool sits idle is to buffer FOUPs in a storage location located near the processing tool (often referred to a “stocker”). Stockers, however, occupy valuable facility floor space. For very high throughput tools, even local stockers (e.g., within the tool bay) may not be fast enough to prevent some tools from sitting idle. This is especially true of tools that only have two load ports. The time to process all the wafers stored in a six wafer FOUP may still be shorter than the time it takes for the system to transport a new FOUP to the tool—even from a nearby storage location. This means that the tool cannot process wafers any faster than the speed of the material transport system.
Therefore, it is desirable to be able to send pods directly from tool to tool, rather than moving through a stocker. This reduces the number of transport moves in the facility, which reduces cycle time and increase throughput. Generally, in order to be able to move FOUPs directly from tool to tool, the tools themselves must have the ability to buffer FOUPs at the tool, which would allow a FOUP to arrive at the tool before the processing tool finishes processing the wafers in the current FOUP, and vice versa.
Therefore, there is a need for a load port to have the ability to store FOUPs while the wafers stored in one or more FOUPs are being processed.